Stilbene derivatives and their use for binding and imaging amyloid plaques

ABSTRACT

This invention relates to a method of imaging amyloid deposits and to labeled compounds, and methods of making labeled compounds useful in imaging amyloid deposits. This invention also relates to compounds, and methods of making compounds for inhibiting the aggregation of amyloid proteins to form amyloid deposits, and a method of delivering a therapeutic agent to amyloid deposits.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional Application No.60/314,658, filed Aug. 27, 2001, the contents of which are fullyincorporated by reference herein.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT

Part of the work performed during development of this invention utilizedU.S. Government funds. The U.S. Government has certain rights in thisinvention under grant numbers NS-18509 and PO1 AG-11542 awarded by theInstitute for the Study of Aging.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel bioactive compounds, methods ofdiagnostic imaging using radiolabeled compounds, and methods of makingradiolabeled compounds.

2. Background Art

Alzheimer's disease (AD) is a progressive neurodegenerative disordercharacterized by cognitive decline, irreversible memory loss,disorientation, and language impairment. Postmortem examination of ADbrain sections reveals abundant senile plaques (SPs) composed ofamyloid-β (Aβ) peptides and numerous neurofibrillary tangles (NFTs)formed by filaments of highly phosphorylated tau proteins (for recentreviews and additional citations see Ginsberg, S. D., et al., “MolecularPathology of Alzheimer's Disease and Related Disorders,” in CerebralCortex: Neurodegenerative and Age-related Changes in Structure andFunction of Cerebral Cortex, Kluwer Academic/Plenum, NY (1999), pp.603–654; Vogelsberg-Ragaglia, V., et al., “Cell Biology of Tau andCytoskeletal Pathology in Alzheimer's Disease,” Alzheimer's Disease,Lippincot, Williams & Wilkins, Philadelphia, Pa. (1999), pp. 359–372).Familial AD (FAD) is caused by multiple mutations in the A precursorprotein (APP), presenilin 1 (PS1) and presenilin 2 (PS2) genes(Ginsberg, S. D., et al., “Molecular Pathology of Alzheimer's Diseaseand Related Disorders,” in Cerebral Cortex: Neurodegenerative andAge-related Changes in Structure and Function of Cerebral Cortex, KluwerAcademic/Plenum, NY (1999), pp. 603–654; Vogelsberg-Ragaglia, V., etal., “Cell Biology of Tau and Cytoskeletal Pathology in Alzheimer'sDisease,” Alzheimer's Disease, Lippincot, Williams & Wilkins,Philadelphia, Pa. (1999), pp. 359–372).

While the exact mechanisms underlying AD are not fully understood, allpathogenic FAD mutations studied thus far increase production of themore amyloidogenic 42–43 amino-acid long form of the Aβ peptide. Thus,at least in FAD, dysregulation of Aβ production appears to be sufficientto induce a cascade of events leading to neurodegeneration. Indeed, theamyloid cascade hypothesis suggests that formation of extracellularfibrillar Aβ aggregates in the brain may be a pivotal event in ADpathogenesis (Selkoe, D. J., “Biology of B-amyloid Precursor Protein andthe Mechanism of Alzheimer's Disease,” Alzheimer's Disease, LippincotWilliams & Wilkins, Philadelphia, Pa. (1999), pp. 293–310; Selkoe, D.J., J. Am. Med. Assoc. 283:1615–1617 (2000); Naslund, J., et al., J. Am.Med. Assoc. 283:1571–1577 (2000); Golde, T. E., et al., Biochimica etBiophysica Acta 1502:172–187 (2000)).

Various approaches in trying to inhibit the production and reduce theaccumulation of fibrillar Aβ in the brain are currently being evaluatedas potential therapies for AD (Skovronsky, D. M. and Lee, V. M., TrendsPharmacol. Sci. 21:161–163 (2000); Vassar, R., et al., Science286:735–741 (1999); Wolfe, M. S., et al., J. Med. Chem. 41:6–9 (1998);Moore, C. L., et al., J. Med. Chem. 43:3434–3442 (2000); Findeis, M. A.,Biochimica et Biophysica Acta 1502:76–84 (2000); Kuner, P., Bohrmann, etal., J. Biol. Chem. 275:1673–1678 (2000)). It is therefore of greatinterest to develop ligands that specifically bind fibrillar Aβaggregates. Since extracellular SPs are accessible targets, these newligands could be used as in vivo diagnostic tools and as probes tovisualize the progressive deposition of Aβ in studies of ADamyloidogenesis in living patients.

To this end, several interesting approaches for developing fibrillar Aβaggregate-specific ligands have been reported (Ashburn, T. T., et al.,Chem. Biol. 3:351–358 (1996); Han, G., et al., J. Am. Chem. Soc.118:4506–4507 (1996); Klunk, W. E., et al., Biol. Psychiatry 35:627(1994); Klunk, W. E., et al., Neurobiol. Aging 16:541–548 (1995); Klunk,W. E., et al., Society for Neuroscience Abstract 23:1638 (1997); Mathis,C. A., et al., Proc. XIIth Intl. Symp. Radiopharm. Chem., Uppsala,Sweden: 94–95 (1997); Lorenzo, A. and Yankner, B. A., Proc. Natl. Acad.Sci. U.S.A. 91:12243–12247 (1994); Zhen, W., et al., J. Med. Chem.42:2805–2815 (1999)). The most attractive approach is based on highlyconjugated chrysamine-G (CG) and Congo red (CR), and the latter has beenused for fluorescent staining of SPs and NFTs in postmortem AD brainsections (Ashburn, T. T., et al., Chem. Biol. 3:351–358 (1996); Klunk,W. E., et al., J. Histochem. Cytochem. 37:1273–1281 (1989)). Theinhibition constants (K_(i)) for binding to fibrillar Aβ aggregates ofCR, CG, and 3′-bromo- and 3′-iodo derivatives of CG are 2,800, 370, 300and 250 nM, respectively (Mathis, C. A., et al., Proc. XIIth Intl. Symp.Radiopharm. Chem., Uppsala, Sweden: 94–95 (1997)). These compounds havebeen shown to bind selectively to Aβ (1–40) peptide aggregates in vitroas well as to fibrillar Aβ deposits in AD brain sections (Mathis, C. A.,et al., Proc. XIIth Intl. Symp. Radiopharm. Chem., Uppsala, Sweden:94–95 (1997)).

Amyloidosis is a condition characterized by the accumulation of variousinsoluble, fibrillar proteins in the tissues of a patient. An amyloiddeposit is formed by the aggregation of amyloid proteins, followed bythe further combination of aggregates and/or amyloid proteins. Formationand accumulation of aggregates of β-amyloid (Aβ) peptides in the brainare critical factors in the development and progression of AD. Thefibrillar aggregates of amyloid peptides, Aβ₁₋₄₀ and Aβ₁₋₄₂, are majormetabolic peptides derived from amyloid precursor protein found insenile plaques and cerebrovascular amyloid deposits in AD patients (Xia,W., et al., J. Proc. Natl. Acad. Sci. U.S.A. 97:9299–9304 (2000)).Prevention and reversal of Aβ plaque formation are being targeted as atreatment for this disease (Selkoe, D., J. JAMA 283:1615–1617 (2000);Wolfe, M. S., et al., J. Med. Chem. 41:6–9 (1998); Skovronsky, D. M.,and Lee, V. M., Trends Pharmacol. Sci. 21:161–163 (2000)).

In addition to the role of amyloid deposits in Alzheimer's disease, thepresence of amyloid deposits has been shown in diseases such asMediterranean fever, Muckle-Wells syndrome, idiopathetic myeloma,amyloid polyneuropathy, amyloid cardiomyopathy, systemic senileamyloidosis, amyloid polyneuropathy, hereditary cerebral hemorrhage withamyloidosis, Down's syndrome, Scrapie, Creutzfeldt-Jacob disease, Kuru,Gerstamnn-Straussler-Scheinker syndrome, medullary carcinoma of thethyroid, Isolated atrial amyloid, β₂-microglobulin amyloid in dialysispatients, inclusion body myositis, β₂-amyloid deposits in muscle wastingdisease, and Islets of Langerhans diabetes Type II insulinoma.

Thus, a simple, noninvasive method for detecting and quantitatingamyloid deposits in a patient has been eagerly sought. Presently,detection of amyloid deposits involves histological analysis of biopsyor autopsy materials. Both methods have drawbacks. For example, anautopsy can only be used for a postmortem diagnosis.

Imaging agents may be based on two types of isotopes. ^(99m)Tc (T_(1/2),6 h; 140 KeV) and ¹²³I (T_(1/2), 13 h; 159 KeV) are routinely used forsingle photon emission computed tomography (SPECT), while ¹¹C (T_(1/2),20 min; 511 KeV) and ¹⁸F (T_(1/2), 110 min; 511 KeV) are commonly usedfor positron emission tomography (PET).

The direct imaging of amyloid deposits in vivo is difficult, as thedeposits have many of the same physical properties (e.g., density andwater content) as normal tissues. Attempts to image amyloid depositsusing magnetic resonance imaging (MRI) and computer-assisted tomography(CAT) have been disappointing and have detected amyloid deposits onlyunder certain favorable conditions. In addition, efforts to labelamyloid deposits with antibodies, serum amyloid P protein, or otherprobe molecules have provided some selectivity on the periphery oftissues, but have provided for poor imaging of tissue interiors.

Potential ligands for detecting Aβ aggregates in the living brain mustcross the intact blood-brain barrier. Thus brain uptake can be improvedby using ligands with relatively smaller molecular size (compared toCongo Red) and increased lipophilicity. Highly conjugated thioflavins (Sand T) are commonly used as dyes for staining the Aβ aggregates in theAD brain (Elhaddaoui, A., et al., Biospectroscopy 1: 351–356 (1995)).These compounds are based on benzothiazole, which is relatively small inmolecular size.

It would be useful to have a noninvasive technique for imaging andquantitating amyloid deposits in a patient. In addition, it would beuseful to have compounds that inhibit the aggregation of amyloidproteins to form amyloid deposits and a method for determining acompound's ability to inhibit amyloid protein aggregation.

SUMMARY OF THE INVENTION

The present invention provides novel compounds of Formula I, II, III IVor V.

The present invention also provides diagnostic compositions comprising aradiolabeled compound of Formula I, II, III, IV or V and apharmaceutically acceptable carrier or diluent.

The invention further provides a method of imaging amyloid depositis,the method comprising introducing into a patient a detectable quantityof a labeled compound of Formula I, II, III, IV or V or apharmaceutically acceptable salt, ester, amide or prodrug thereof.

The present invention also provides a method for inhibiting theaggregation of amyloid proteins, the method comprising administering toa mammal an amyloid inhibiting amount of a compound Formula I, II, III,IV or V or a pharmaceutically acceptable salt, ester, amide, or prodrugthereof.

A further aspect of this invention is directed to methods andintermediates useful for synthesizing the amyloid inhibiting and imagingcompounds of Formula I, II, III, IV or V described herein.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1, 3, 4 and 5 depict representative compounds of the presentinvention and the binding data for these compounds.

FIG. 2 depicts the binding data for a compound of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A first aspect of the present invention is directed to compounds ofFormula I:

or a pharmaceutically acceptable salt thereof, wherein:

-   -   R⁵ is hydrogen or C₁₋₄ alkyl;    -   R¹, R² and R³, in each instance, is independently selected from        the group consisting of hydrogen, halogen, C₁₋₄ alkyl, cyano,        carboxy(C₁₋₅)alkyl, trifluoromethyl, nitro, methylamino,        dimethylamino, halo(C₁₋₄)alkyl, and formyl;    -   R⁴ is selected from the group consisting of:        -   a. C₁₋₄ alkylthio,        -   b. halo(C₁₋₄)alkoxy,        -   c. carboxy(C₁₋₅)alkyl,        -   d. hydroxy,        -   e. C₁₋₄ alkoxy,        -   f. NR⁶R⁷, wherein            -   R⁶ and R⁷ are hydrogen, halo(C₁₋₄)alkyl or C₁₋₄ alkyl,        -   g. phenyl(C₁₋₄)alkyl,        -   h. C₆₋₁₀ aryl,        -   i. heteroaryl,        -   j. heterocycle,        -   k. heterocycle(C₁₋₄)alkyl, and        -   l. C₃₋₆ cycloalkyl,            -   wherein said phenyl(C₁₋₄)alkyl, C₆₋₁₀ aryl, heteroaryl,                heterocycle, heterocycle(C₁₋₄)alkyl or C₃₋₆ cycloalkyl                is substituted with one of the following: C₁₋₄                alkylthio, C₁₋₄ alkyl sulfonyl, methoxy, hydroxy,                dimethylamino or methylamino;                and,    -   X′ is ¹²⁵I, ¹²³I, ¹³¹I, ¹⁸F, ¹⁸Fluoro(C₁₋₄)alkyl,        [¹⁸Fluoro(C₁₋₄)alkyl]alkylamino, [¹⁸Fluoro(C₁₋₄)alkyl]amino,        ⁷⁶Br, ⁷⁷Br or Sn(alkyl)₃.

Useful compounds falling within the scope of Formula I include compoundswherein R⁵ is hydrogen or C₁₋₄ alkyl. Especially useful values of R⁵ arehydrogen and methyl. The most useful value of R⁵ is hydrogen.

Useful compounds are those of Formula I wherein R¹, R² and R³, in eachinstance, is independently selected from the group as described above.Preferably, R³ is hydrogen. In this preferred embodiment, it isespecially preferred that R¹ and R² are independently selected from thegroup consisting of hydrogen and C₁₋₄ alkyl. More preferably, at leastone of R¹ and R² is hydrogen. Most preferably, R¹ and R² are hydrogen.

Useful compounds of Formula I also include those compounds wherein R⁴ isas described above. Preferable values of R⁴ under the scope of C₆₋₁₀aryl include phenyl, naphthyl or tetrahydronaphthyl. Preferable valuesof R⁴ under the scope of heteroaryl include thienyl, furyl, pyranyl,pyrrolyl, pyridinyl, indolyl, and imidazolyl. Preferable values of R⁴under the scope of heterocycle include piperidinyl, pyrrolidinyl, andmorpholinyl. In compounds wherein R⁴ is a preferred embodiment of aC₆₋₁₀ aryl, heteroaryl, heterocycle, heterocycle(C₁₋₄)alkyl or C₃₋₆cycloalkyl, it is most preferable that the ring is substituted with oneof the following: C₁₋₄ alkylthio, carboxy(C₁₋₅)alkyl, hydroxy, methoxy,dimethylamino or methylamino. In another embodiment, R⁴ is morepreferably selected from the group consisting of C₁₋₄ alkylthio,halo(C₁₋₄)alkoxy, carboxy(C₁₋₅)alkyl, hydroxy, C₁₋₄ alkoxy, and NR⁶R⁷,wherein R⁶ and R⁷ are independently hydrogen, halo(C₁₋₄)alkyl or C₁₋₄alkyl. Most preferably, R⁴ is selected from the group consisting ofmethylthio, carboxymethyl, carboxyethyl, carboxypropyl, hydroxy,methoxy, or NR⁶R⁷, wherein R⁶ and R⁷ are independently hydrogen,fluoro(C₁₋₄)alkyl or methyl.

Useful values of X′ include ¹²⁵I, ¹²³I, ¹³¹I, ¹⁸F, ¹⁸Fluoro(C₁₋₄)alkyl,[¹⁸Fluoro(C₁₋₄)alkyl]alkylamino, [¹⁸Fluoro(C₁₋₄)alkyl]amino, ⁷⁶Br, ⁷⁷Bror Sn(alkyl)₃. Especially useful values of X′ are ¹²³I, ¹⁸Fluoromethyl,¹⁸Fluoroethyl and ¹⁸Fluoropropyl.

The present invention is also directed to compounds of Formula II:

or a pharmaceutically acceptable salt thereof,

-   -   Z is O, S or NR^(a), wherein        -   R^(a) is C₁₋₄ alkyl;    -   R⁹, R¹⁰ and R¹¹, in each instance, is independently selected        from the group consisting of hydrogen, halogen, C₁₋₄ alkyl,        cyano, carboxy(C₁₋₅)alkyl, trifluoromethyl, nitro, methylamino,        dimethylamino, halo(C₁₋₄)alkyl, and formyl;    -   R¹² is selected from the group consisting of:        -   a. C₁₋₄ alkylthio,        -   b. halo(C₁₋₄)alkoxy,        -   c. carboxy(C₁₋₅)alkyl,        -   d. hydroxy,        -   e. C₁₋₄ alkoxy,        -   f. NR¹³R¹⁴, wherein            -   R¹³ and R¹⁴ are hydrogen, halo(C₁₋₄)alkyl or C₁₋₄ alkyl,        -   g. phenyl(C₁₋₄)alkyl,        -   h. C₆₋₁₀ aryl,        -   i. heteroaryl,        -   j. heterocycle,        -   k. heterocycle(C₁₋₄)alkyl, and        -   l. C₃₋₆ cycloalkyl,            -   wherein said phenyl(C₁₋₄)alkyl, C₆₋₁₀ aryl, heteroaryl,                heterocycle, heterocycle(C₁₋₄)alkyl or C₃₋₆ cycloalkyl                is substituted with one of the following: C₁₋₄                alkylthio, C₁₋₄ alkyl sulfonyl, methoxy, hydroxy,                dimethylamino or methylamino;                and,    -   X′ is ¹²⁵I, ¹²³I, ¹³¹I, ¹⁸F, ¹⁸Fluoro(C₁₋₄)alkyl,        [¹⁸Fluoro(C₁₋₄)alkyl]alkylamino, [¹⁸Fluoro(C₁₋₄)alkyl]amino,        ⁷⁶Br, ⁷⁷Br or Sn(alkyl)₃.

Useful compounds falling within the scope of Formula II includecompounds wherein Z is O, S or NR^(a), wherein R^(a) is C₁₋₄ alkyl.Especially useful compounds are those wherein Z is O.

Useful compounds are those of Formula I wherein R⁹, R¹⁰ and R¹¹, in eachinstance, is independently selected from the group as described above.Preferably, R¹¹ is hydrogen. In this preferred embodiment, it isespecially preferred that R⁹ and R¹⁰ are independently selected from thegroup consisting of hydrogen and C₁₋₄ alkyl. More preferably, at leastone of R⁹ and R¹⁰ is hydrogen. Most preferably, R⁹ and R¹⁰ are hydrogen.

Useful compounds of Formula I also include those compounds wherein R¹²is as described above. Preferable values of R¹² under the scope of C₆₋₁₀aryl include phenyl, naphthyl or tetrahydronaphthyl. Preferable valuesof R¹² under the scope of heteroaryl include thienyl, furyl, pyranyl,pyrrolyl, pyridinyl, indolyl, and imidazolyl. Preferable values of R¹²under the scope of heterocycle include piperidinyl, pyrrolidinyl, andmorpholinyl. In compounds wherein R¹² is a preferred embodiment of aC₆₋₁₀ aryl, heteroaryl, heterocycle, heterocycle(C₁₋₄)alkyl or C₃₋₆cycloalkyl, it is most preferable that the ring is substituted with oneof the following: C₁₋₄ alkylthio, carboxy(C₁₋₅)alkyl, methoxy, hydroxy,dimethylamino or methylamino. In another embodiment, R¹² is morepreferably selected from the group consisting of C₁₋₄ alkylthio,halo(C₁₋₄)alkoxy, carboxy(C₁₋₅)alkyl, hydroxy, C₁₋₄ alkoxy, and NR¹³R¹⁴,wherein R¹³ and R¹⁴ are independently hydrogen, halo(C₁₋₄)alkyl orC₁₋₄alkyl. Most preferably, R¹² is selected from the group consisting ofmethylthio, carboxymethyl, carboxyethyl, carboxypropyl, hydroxy,methoxy, or NR¹³R¹⁴, wherein R¹³ and R¹⁴ are independently hydrogen,fluoro(C₁₋₄)alkyl or methyl.

Useful values of X′ include ¹²⁵I, ¹²³I, ¹³¹I, ¹⁸F, ¹⁸Fluoro(C₁₋₄)alkyl,[¹⁸Fluoro(C₁₋₄)alkyl]alkylamino, [¹⁸Fluoro(C₁₋₄)alkyl]amino, ⁷⁶Br, ⁷⁷Bror Sn(alkyl)₃. Especially useful values of X′ are ¹²³I, ¹⁸Fluoromethyl,¹⁸Fluoroethyl and ¹⁸Fluoropropyl.

Another aspect of the present invention is directed to compounds ofFormula III:

or a pharmaceutically acceptable salt thereof, wherein:

-   -   n is equal to a number from zero to four,    -   R²⁸ is hydrogen or C₁₋₄ alkyl,    -   Z is O, S or —CR¹⁵═CR¹⁶—, wherein    -   R¹⁵, R¹⁶, R¹⁷, R¹⁸, R¹⁹, R²⁰, R²¹, R²², R²³, R²⁴ and R²⁵ in each        instance, is independently selected from the group consisting of        hydrogen, halogen, Sn(alkyl)₃, C₁₋₄ alkyl, C₁₋₄ alkyl sulfanyl,        C₁₋₄ alkyl sulfonyl, C₁₋₄ alkoxy, hydroxy, C₆₋₁₀ aryl,        carboxyalkyl, carboxy and NR²⁶R²⁷, wherein        -   R²⁶ and R²⁷ are independently hydrogen, C₁₋₄ alkyl,            phenyl(C₁₋₄)alkyl, halo(C₁₋₄)alkyl, haloaryl(C₁₋₄)alkyl,            C₆₋₁₀ aryl, heteroaryl, heterocycle, heterocycle(C₁₋₄)alkyl            or C₃₋₆ cycloalkyl, wherein            -   said C₆₋₁₀ aryl, C₆₋₁₀ heteroaryl, heterocycle or C₃₋₆                cycloalkyl is unsubstituted or substituted with one of                the following: C₁₋₄ alkylthio, C₁₋₄ alkyl sulfonyl,                methoxy, hydroxy, dimethylamino or methylamino,                and,    -   R^(P) is hydrogen or a sulfur protecting group, such as        methoxymethyl, methoxyethoxymethyl, p-methoxybenzyl or benzyl.

The tetradentate metal ligand moiety of Formula III is capable ofcomplexing with a metal, such as 99m-pertechnetate, as described hereinto form metal chelates, exemplified by the following Formula:

Additionally, a rhenium radioisotope can be complexed with thetetradentate metal ligand.

Useful compounds of Formula III are those compounds wherein Z is O, S or—CR¹⁵═CR¹⁶—, wherein R¹⁵ and R¹⁶ are as described above. Preferably, Zis —CR¹⁵═CR¹⁶—, wherein R¹⁵ and R¹⁶ are as described above. Morepreferably, R¹⁵ and R¹⁶ are hydrogen.

Useful compounds of the present invention are those compounds whereinR¹⁷ through R²⁵ are as defined above. Preferable values of R¹⁷ throughR²⁵ falling under the scope of C₆₋₁₀ aryl include phenyl, naphthyl ortetrahydronaphthyl. Preferable values of R¹⁷ through R²⁵ falling underthe scope of heteroaryl include thienyl, furyl, pyranyl, pyrrolyl,pyridinyl, indolyl, and imidazolyl. Preferable values of R¹⁷ through R²⁵falling under the scope of heterocycle include piperidinyl,pyrrolidinyl, and morpholinyl. In compounds wherein R¹⁷ through R²⁵ area preferred embodiment of a C₆₋₁₀ aryl, heteroaryl, heterocycle,heterocycle(C₁₋₄)alkyl or C₃₋₆ cycloalkyl, it is most preferable thatthe ring is substituted with one of the following: C₁₋₄ alkylthio, C₁₋₄alkyl sulfonyl, methoxy, hydroxy, dimethylamino or methylamino. Inanother embodiment, more preferred compounds include those compoundswherein one or more of R¹⁷ through R²⁵ is hydrogen. In this embodiment,it is preferred that R¹⁷ is other than hydrogen. More preferably, R¹⁷ isselected from the group consisting C₁₋₄ alkylthio, C₁₋₄ alkyl sulfonyl,hydroxy, C₁₋₄ alkoxy, NR²⁶R²⁷, wherein R²⁶ and R²⁷ are independentlyhydrogen or C₁₋₄ alkyl. Most preferably, R¹⁷ is NR²⁶R²⁷, wherein R²⁶ andR²⁷ are methyl.

Useful compounds also include those of Formula III wherein n is equal toa number from zero to four. Preferably, n is equal to a number from zeroto two. More preferably, n is equal to zero.

A further aspect of the present invention is directed to compounds ofFormula IV:

or a pharmaceutically acceptable salt thereof, wherein

-   -   n is equal to a number between zero and four,    -   R²⁹, R³⁰, R³¹, R³², R³³, R³⁴ and R³⁵ are independently selected        from the group consisting of:    -   a. hydrogen,    -   b. C₁₋₄ alkylthio,    -   c. C₁₋₄ alkylsulfonyl,    -   d. hydroxy,    -   e. C₁₋₄alkoxy,    -   f. NR⁶R⁷, wherein        -   R⁶ and R⁷ are hydrogen or C₁₋₄ alkyl,    -   g. phenyl(C₁₋₄)alkyl,    -   h. C₆₋₁₀ aryl,    -   i. heteroaryl,    -   j. heterocycle,    -   k. heterocycle(C₁₋₄)alkyl, and    -   l. C₃₋₆ cycloalkyl,        -   wherein said phenyl(C₁₋₄)alkyl, C₆₋₁₀ aryl, heteroaryl,            heterocycle, heterocycle(C₁₋₄)alkyl or C₃₋₆ cycloalkyl is            substituted with one of the following: C₁₋₄ alkylthio, C₁₋₄            alkyl sulfonyl, methoxy, hydroxy, dimethylamino or            methylamino;    -   provided that one of R²⁹ through R³⁵ is monoalkylaminophenyl or        dialkylaminophenyl; and    -   R^(P) is hydrogen or a sulfur protecting group, such as        methoxymethyl, methoxyethoxymethyl, p-methoxybenzyl or benzyl.

Useful compounds of Formula IV are those compounds wherein R²⁹, R³⁰,R³¹, R³², R³³, R³⁴ and R³⁵ are as described above. Preferable values ofR²⁹ through R³⁵ falling under the scope of C₆₋₁₀ aryl include phenyl,naphthyl or tetrahydronaphthyl. Preferable values of R²⁹ through R³⁵falling under the scope of heteroaryl include thienyl, furyl, pyranyl,pyrrolyl, pyridinyl, indolyl and imidazolyl. Preferable values of R²⁹through R³⁵ falling under the scope of heterocycle include piperidinyl,pyrrolidinyl, and morpholinyl. In compounds wherein R²⁹ through R³⁵ area preferred embodiment of a C₆₋₁₀ aryl, heteroaryl, heterocycle,heterocycle(C₁₋₄)alkyl or C₃₋₆ cycloalkyl, it is most preferable thatthe ring is substituted with one of the following: C₁₋₄ alkylthio, C₁₋₄alkyl sulfonyl, methoxy, hydroxy, dimethylamino or methylamino. Inanother embodiment, especially useful compounds are those wherein R²⁹,R³⁰, R³¹, and R³³ are hydrogen. Within this embodiment, it is especiallypreferred that one of R³² and R³⁴ is as described above, the other ofR³² and R³⁴ is hydrogen. More preferably, one of R³² and R³⁴ isaminophenyl, monoalkylaminophenyl or dialkylaminophenyl, the other ofR³² and R³⁴ is hydrogen. Most preferably, one of R³² and R³⁴ isdimethylaminophenyl, the other of R³² and R³⁴ is hydrogen. Useful valuesof R³⁵ also include hydrogen, methoxy, C₁₋₄ alkylthio, C₁₋₄ alkylsulfonyl, hydroxy and C₁₋₄ alkyl. Most preferably, R³⁵ is hydrogen orC₁₋₄ alkyl.

Useful compounds of Formula IV also include compounds wherein n is equalto a number from zero to four. More preferably, n is equal to zero orone. Most preferably, n is equal to zero.

It is also to be understood that the present invention is considered toinclude stereoisomers as well as optical isomers, e.g. mixtures ofenantiomers as well as individual enantiomers and diastereomers, whicharise as a consequence of structural asymmetry in selected compounds ofthe present series.

The compounds of Formula I, II, III or IV may also be solvated,especially hydrated. Hydration may occur during manufacturing of thecompounds or compositions comprising the compounds, or the hydration mayoccur over time due to the hygroscopic nature of the compounds. Inaddition, the compounds of the present invention can exist in unsolvatedas well as solvated forms with pharmaceutically acceptable solvents suchas water, ethanol, and the like. In general, the solvated forms areconsidered equivalent to the unsolvated forms for the purposes of thepresent invention.

A further aspect of this invention is directed to compounds of FormulaV:

or a pharmaceutically acceptable salt thereof or a derivative ofcompound of Formula V containing a radioisotope complex, wherein:

-   -   R is C₁₋₄ alkyl or is as defined for R²⁹–R³⁵ above, and    -   R^(P) is as defined above.

When any variable occurs more than one time in any constituent or inFormula I, II, III, IV or V its definition on each occurrence isindependent of its definition at every other occurrence. Alsocombinations of substituents and/or variables are permissible only ifsuch combinations result in stable compounds.

The term “alkyl” as employed herein by itself or as part of anothergroup refers to both straight and branched chain radicals of up to 8carbons, preferably 6 carbons, more preferably 4 carbons, such asmethyl, ethyl, propyl, isopropyl, butyl, t-butyl, and isobutyl.

The term “alkoxy” is used herein to mean a straight or branched chainalkyl radical, as defined above, unless the chain length is limitedthereto, bonded to an oxygen atom, including, but not limited to,methoxy, ethoxy, n-propoxy, isopropoxy, and the like. Preferably thealkoxy chain is 1 to 6 carbon atoms in length, more preferably 1–4carbon atoms in length.

The term “monoalkylamine” as employed herein by itself or as part ofanother group refers to an amino group which is substituted with onealkyl group as defined above.

The term “dialkylamine” as employed herein by itself or as part ofanother group refers to an amino group which is substituted with twoalkyl groups as defined above.

The term “halo” employed herein by itself or as part of another grouprefers to chlorine, bromine, fluorine or iodine.

The term “haloalkyl” as employed herein refers to any of the above alkylgroups substituted by one or more chlorine, bromine, fluorine or iodinewith fluorine and chlorine being preferred, such as chloromethyl,iodomethyl, trifluoromethyl, 2,2,2-trifluoroethyl, and 2-chloroethyl.

The term “alkylthio” as employed herein by itself or as part of anothergroup refers to a thioether of the structure: R—S, wherein R is a C₁₋₄alkyl as defined above.

The term “alkylsulfonyl” as employed herein by itself or as part ofanother group refers to a sulfone of the structure: R—SO₂, wherein R isa C₁₋₄ alkyl as defined above.

The term “aryl” as employed herein by itself or as part of another grouprefers to monocyclic or bicyclic aromatic groups containing from 6 to 12carbons in the ring portion, preferably 6–10 carbons in the ringportion, such as phenyl, naphthyl or tetrahydronaphthyl.

The term “heterocycle” or “heterocyclic ring”, as used herein exceptwhere noted, represents a stable 5- to 7-membered mono-heterocyclic ringsystem which may be saturated or unsaturated, and which consists ofcarbon atoms and from one to three heteroatoms selected from the groupconsisting of N, O, and S, and wherein the nitrogen and sulfurheteroatom may optionally be oxidized. Especially useful are ringscontain one nitrogen combined with one oxygen or sulfur, or two nitrogenheteroatoms. Examples of such heterocyclic groups include piperidinyl,pyrrolyl, pyrrolidinyl, imidazolyl, imidazinyl, imidazolidinyl, pyridyl,pyrazinyl, pyrimidinyl, oxazolyl, oxazolidinyl, isoxazolyl,isoxazolidinyl, thiazolyl, thiazolidinyl, isothiazolyl, homopiperidinyl,homopiperazinyl, pyridazinyl, pyrazolyl, and pyrazolidinyl, mostpreferably thiamorpholinyl, piperazinyl, and morpholinyl.

The term “heteroatom” is used herein to mean an oxygen atom (“O”), asulfur atom (“S”) or a nitrogen atom (“N”). It will be recognized thatwhen the heteroatom is nitrogen, it may form an NR^(a)R^(b) moiety,wherein R^(a) and R^(b) are, independently from one another, hydrogen orC₁₋₄ alkyl, C₂₋₄ aminoalkyl, C₁₋₄ halo alkyl, halo benzyl, or R¹ and R²are taken together to form a 5- to 7-member heterocyclic ring optionallyhaving O, S or NR^(c) in said ring, where R^(c) is hydrogen or C₁₋₄alkyl.

The term “heteroaryl” as employed herein refers to groups having 5 to 14ring atoms; 6, 10 or 14 π electrons shared in a cyclic array; andcontaining carbon atoms and 1, 2 or 3 oxygen, nitrogen or sulfurheteroatoms (where examples of heteroaryl groups are: thienyl,benzo[b]thienyl, naphtho[2,3-b]thienyl, thianthrenyl, furyl, pyranyl,isobenzofuranyl, benzoxazolyl, chromenyl, xanthenyl, phenoxathiinyl,2H-pyrrolyl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl,pyrimidinyl, pyridazinyl, indolizinyl, isoindolyl, 3H-indolyl, indolyl,indazolyl, purinyl, 4H-quinolizinyl, isoquinolyl, quinolyl,phthalazinyl, naphthyridinyl, quinazolinyl, cinnolinyl, pteridinyl,4aH-carbazolyl, carbazolyl, β-carbolinyl, phenanthridinyl, acridinyl,perimidinyl, phenanthrolinyl, phenazinyl, isothiazolyl, phenothiazinyl,isoxazolyl, furazanyl and phenoxazinyl groups).

The term “aralkyl” or “arylalkyl” as employed herein by itself or aspart of another group refers to C₁₋₆alkyl groups as discussed abovehaving an aryl substituent, such as benzyl, phenylethyl or2-naphthylmethyl.

Another aspect of this invention is related to methods of preparingcompounds of Formula I, II, III, IV or V.

In embodiments of Formulae III, IV or V, the groups R^(P) are bothhydrogen, or can be any of the variety of protecting groups availablefor sulfur, including methoxymethyl, methoxyethoxymethyl,p-methoxybenzyl or benzyl. Sulfur protecting groups are described indetail in Greene, T. W. and Wuts, P. G. M., Protective Groups in OrganicSynthesis, 2nd Edition, John Wiley and Sons, Inc., New York (1991).Protecting group R^(P) can be removed by appropriate methods well knownin the art of organic synthesis, such as trifluoroacetic acid, mercuricchloride or sodium in liquid ammonia. In the case of Lewis acid labilegroups, including acetamidomethyl and benzamidomethyl, R^(P) can be leftintact. Labeling of the ligand with technetium in this case will cleavethe protecting group, rendering the protected diaminedithiol equivalentto the unprotected form.

Tc-99m complexes can be prepared as follows. A small amount ofnon-radiolabeled compound (1–2 mg) is dissolved in 100 μL EtOH and mixedwith 200 μL HCl (1 N) and 1 mL Sn-glucoheptonate solution (containing8–32 μg SnCl₂ and 80–320 μg Na-glucoheptonate, pH 6.67) and 50 μL EDTAsolution (0.1 N). [^(99m)Tc]Pertechnetate (100–200 μL; ranging from 2–20mCi) saline solution are then added. The reaction is heated for 30 minat 100° C., then cooled to room temperature. The reaction mixture isanalyzed on TLC (EtOH:conc. NH₃ 9:1) for product formation and puritycheck. The mixture can be neutralized with phosphate buffer to pH 5.0.

The present invention further relates to a method of preparing atechnetium-99m complex according to the present invention by reactingtechnetium-99m in the form of a pertechnetate in the presence of areducing agent and optionally a suitable chelator with an appropriateCh-containing compound.

The reducing agent serves to reduce the Tc-99m pertechnetate which iseluted from a molybdenum-technetium generator in a physiological salinesolution. Suitable reducing agents are, for example, dithionite,formamidine sulphinic acid, diaminoethane disulphinate or suitablemetallic reducing agents such as Sn(II), Fe(II), Cu(I), Ti(III) orSb(III). Sn(II) has proven to be particularly suitable.

For the above-mentioned complex-forming reaction, technetium-99m isreacted with an appropriate compound of the invention as a salt or inthe form of technetium bound to comparatively weak chelators. In thelatter case the desired technetium-99m complex is formed by ligandexchange. Examples of suitable chelators for the radionuclide aredicarboxylic acids, such as oxalic acid, malonic acid, succinic acid,maleic acid, orthophtalic acid, malic acid, lactic acid, tartaric acid,citric acid, ascorbic acid, salicylic acid or derivatives of theseacids; phosphorus compounds such as pyrophosphates; or enolates. Citricacid, tartaric acid, ascorbic acid, glucoheptonic acid or a derivativethereof are particularly suitable chelators for this purpose, because achelate of technetium-99m with one of these chelators undergoes thedesired ligand exchange particularly easily.

The most commonly used procedure for preparing [Tc^(v)O]⁺³N₂S₂ complexesis based on stannous (II) chloride reduction of [^(99m)Tc]pertechnetate,the common starting material. The labeling procedure normally relies ona Tc-99m ligand exchange reaction between Tc-99m (Sn)-glucoheptonate andthe N₂S₂ ligand. Preparation of stannous (II) chloride and preserving itin a consistent stannous (II) form is critically important for thesuccess of the labeling reaction. To stabilize the air-sensitivestannous ion it is a common practice in nuclear medicine to use alyophilized kit, in which the stannous ion is in a lyophilized powderform mixed with an excess amount of glucoheptonate under an inert gaslike nitrogen or argon. The preparation of the lyophilized stannouschloride/sodium glucoheptonate kits ensures that the labeling reactionis reproducible and predictable. The N₂S₂ ligands are usuallyair-sensitive (thiols are easily oxidized by air) and there aresubsequent reactions which lead to decomposition of the ligands. Themost convenient and predictable method to preserve the ligands is toproduce lyophilized kits containing 100–500 μg of the ligands underargon or nitrogen.

The present invention is further directed to methods of preparingcompounds of the above Formula I, II, III, IV or V. The compounds ofthis invention can be prepared by reactions described in Schemes 1–9.

Schemes 1–5 depict a synthetic route for forming stilbene derivatives ofFormula I using a Wittig reagent.

Scheme 6 depicts a synthetic route for forming derivatives of FormulaII.

Scheme 7 depicts a synthetic route for forming derivatives of FormulaIII.

Scheme 8 depicts a synthetic route for derivatives of Formula IV.

Scheme 9 depicts a synthetic route for forming derivatives of FormulaIV.

Schemes 10 and 11 depict synthetic routes for forming derivatives ofFormula I.

Scheme 12 depicts a synthetic route for forming intermediates of FormulaV.

Scheme 13 depicts a synthetic route for forming derivatives of FormulaV.

When the compounds of this invention are to be used as imaging agents,they must be labeled with suitable radioactive halogen isotopes.Although ¹²⁵I-isotopes are useful for laboratory testing, they willgenerally not be useful for actual diagnostic purposes because of therelatively long half-life (60 days) and low gamma-emission (30–65 Kev)of ¹²⁵I. The isotope ¹²³I has a half life of thirteen hours and gammaenergy of 159 KeV, and it is therefore expected that labeling of ligandsto be used for diagnostic purposes would be with this isotope. Otherisotopes which may be used include ¹³¹I (half life of 2 hours). Suitablebromine isotopes include ⁷⁷Br and ⁷⁶Br.

The radiohalogenated compounds of this invention lend themselves easilyto formation from materials which could be provided to users in kits.Kits for forming the imaging agents can contain, for example, a vialcontaining a physiologically suitable solution of an intermediate ofFormula I, II, III, IV or V in a concentration and at a pH suitable foroptimal complexing conditions. The user would add to the vial anappropriate quantity of the radioisotope, e.g., Na¹²³I, and an oxidant,such as hydrogen peroxide. The resulting labeled ligand may then beadministered intravenously to a patient, and receptors in the brainimaged by means of measuring the gamma ray or photo emissions therefrom.

Since the radiopharmaceutical composition according to the presentinvention can be prepared easily and simply, the preparation can becarried out readily by the user. Therefore, the present invention alsorelates to a kit, comprising:

(1) A non-radiolabeled compound of the invention, the compoundoptionally being in a dry condition; and also optionally having aninert, pharmaceutically acceptable carrier and/or auxiliary substancesadded thereto; and

(2) a reducing agent and optionally a chelator;

wherein ingredients (1) and (2) may optionally be combined; and furtherwherein instructions for use with a prescription for carrying out theabove-described method by reacting ingredients (1) and (2) withtechnetium-99m in the form of a pertechnetate solution may be optionallyincluded.

Examples of suitable reducing agents and chelators for the above kithave been listed above. The pertechnetate solution can be obtained bythe user from a molybdenum-technetium generator. Such generators areavailable in a number of institutions that perform radiodiagnosticprocedures. As noted above the ingredients (1) and (2) may be combined,provided they are compatible. Such a monocomponent kit, in which thecombined ingredients are preferably lyophilized, is excellently suitableto be reacted by the user with the pertechnetate solution in a simplemanner.

When desired, the radioactive diagnostic agent may contain any additivesuch as pH controlling agents (e.g., acids, bases, buffers), stabilizers(e.g., ascorbic acid) or isotonizing agents (e.g., sodium chloride).

The term “pharmaceutically acceptable salt” as used herein refers tothose carboxylate salts or acid addition salts of the compounds of thepresent invention which are, within the scope of sound medicaljudgement, suitable for use in contact with the tissues of patientswithout undue toxicity, irritation, allergic response, and the like,commensurate with a reasonable benefit/risk ratio, and effective fortheir intended use, as well as the zwitterionic forms, where possible,of the compounds of the invention. The term “salts” refers to therelatively nontoxic, inorganic and organic acid addition salts ofcompounds of the present invention. Also included are those saltsderived from non-toxic organic acids such as aliphatic mono anddicarboxylic acids, for example acetic acid, phenyl-substituted alkanoicacids, hydroxy alkanoic and alkanedioic acids, aromatic acids, andaliphatic and aromatic sulfonic acids. These salts can be prepared insitu during the final isolation and purification of the compounds or byseparately reacting the purified compound in its free base form with asuitable organic or inorganic acid and isolating the salt thus formed.Further representative salts include the hydrobromide, hydrochloride,sulfate, bisulfate, nitrate, acetate, oxalate, valerate, oleate,palmitate, stearate, laurate, borate, benzoate, lactate, phosphate,tosylate, citrate, maleate, fumarate, succinate, tartrate, naphthylatemesylate, glucoheptonate, lactiobionate and laurylsulphonate salts,propionate, pivalate, cyclamate, isethionate, and the like. These mayinclude cations based on the alkali and alkaline earth metals, such assodium, lithium, potassium, calcium, magnesium, and the like, as wellas, nontoxic ammonium, quaternary ammonium and amine cations including,but not limited to ammonium, tetramethylammonium, tetraethylammonium,methylamine, dimethylamine, trimethylamine, triethylamine, ethylamine,and the like. (See, for example, Berge S. M., et al., PharmaceuticalSalts, J. Pharm. Sci. 66:1–19 (1977) which is incorporated herein byreference.)

In the first step of the present method of imaging, a labeled compoundof Formula I, II, III, IV or V is introduced into a tissue or a patientin a detectable quantity. The compound is typically part of apharmaceutical composition and is administered to the tissue or thepatient by methods well known to those skilled in the art.

For example, the compound can be administered either orally, rectally,parenterally (intravenous, by intramuscularly or subcutaneously),intracisternally, intravaginally, intraperitoneally, intravesically,locally (powders, ointments or drops), or as a buccal or nasal spray.

In a preferred embodiment of the invention, the labeled compound isintroduced into a patient in a detectable quantity and after sufficienttime has passed for the compound to become associated with amyloiddeposits, the labeled compound is detected noninvasively inside thepatient. In another embodiment of the invention, a labeled compound ofFormula I, II, III, IV or V is introduced into a patient, sufficienttime is allowed for the compound to become associated with amyloiddeposits, and then a sample of tissue from the patient is removed andthe labeled compound in the tissue is detected apart from the patient.In a third embodiment of the invention, a tissue sample is removed froma patient and a labeled compound of Formula I, II, III, IV or V isintroduced into the tissue sample. After a sufficient amount of time forthe compound to become bound to amyloid deposits, the compound isdetected.

The administration of the labeled compound to a patient can be by ageneral or local administration route. For example, the labeled compoundmay be administered to the patient such that it is delivered throughoutthe body. Alternatively, the labeled compound can be administered to aspecific organ or tissue of interest. For example, it is desirable tolocate and quantitate amyloid deposits in the brain in order to diagnoseor track the progress of Alzheimer's disease in a patient.

The term “tissue” means a part of a patient's body. Examples of tissuesinclude the brain, heart, liver, blood vessels, and arteries. Adetectable quantity is a quantity of labeled compound necessary to bedetected by the detection method chosen. The amount of a labeledcompound to be introduced into a patient in order to provide fordetection can readily be determined by those skilled in the art. Forexample, increasing amounts of the labeled compound can be given to apatient until the compound is detected by the detection method ofchoice. A label is introduced into the compounds to provide fordetection of the compounds.

The term “patient” means humans and other animals. Those skilled in theart are also familiar with determining the amount of time sufficient fora compound to become associated with amyloid deposits. The amount oftime necessary can easily be determined by introducing a detectableamount of a labeled compound of Formula I, II, III, IV or V into apatient and then detecting the labeled compound at various times afteradministration.

The term “associated” means a chemical interaction between the labeledcompound and the amyloid deposit. Examples of associations includecovalent bonds, ionic bonds, hydrophilic-hydrophilic interactions,hydrophobic-hydrophobic interactions, and complexes.

Those skilled in the art are familiar with the various ways to detectlabeled compounds. For example, magnetic resonance imaging (MRI),positron emission tomography (PET), or single photon emission computedtomography (SPECT) can be used to detect radiolabeled compounds. Thelabel that is introduced into the compound will depend on the detectionmethod desired. For example, if PET is selected as a detection method,the compound must possess a positron-emitting atom, such as ¹¹C or ¹⁸F.

The radioactive diagnostic agent should have sufficient radioactivityand radioactivity concentration which can assure reliable diagnosis. Forinstance, in case of the radioactive metal being technetium-99m, it maybe included usually in an amount of 0.1 to 50 mCi in about 0.5 to 5.0 mlat the time of administration. The amount of a compound of Formula I,II, III, IV or V may be such as sufficient to form a stable chelatecompound with the radioactive metal.

The thus formed chelate compound as a radioactive diagnostic agent issufficiently stable, and therefore it may be immediately administered assuch or stored until its use. When desired, the radioactive diagnosticagent may contain any additive such as pH controlling agents (e.g.,acids, bases, buffers), stabilizers (e.g., ascorbic acid) or isotonizingagents (e.g., sodium chloride).

The imaging of amyloid deposits can also be carried out quantitativelyso that the amount of amyloid deposits can be determined.

Preferred compounds for imaging include a radioisotope such as ¹²³I,¹²⁵I, ¹³¹I, ¹⁸F, ⁷⁶Br or ⁷⁷Br.

The present invention is also directed at a method of imaging amyloiddeposits. One of the key prerequisites for an in vivo imaging agent ofthe brain is the ability to cross the intact blood-brain barrier after abolus iv injection.

Another aspect of the invention is a method of inhibiting amyloid plaqueaggregation. The present invention also provides a method of inhibitingthe aggregation of amyloid proteins to form amyloid deposits, byadministering to a patient an amyloid inhibiting amount of a compound ofthe above Formula I, II, III, IV or V.

Those skilled in the art are readily able to determine an amyloidinhibiting amount by simply administering a compound of Formula I, II,III, IV or V to a patient in increasing amounts until the growth ofamyloid deposits is decreased or stopped. The rate of growth can beassessed using imaging as described above or by taking a tissue samplefrom a patient and observing the amyloid deposits therein. The compoundsof the present invention can be administered to a patient at dosagelevels in the range of about 0.1 to about 1,000 mg per day. For a normalhuman adult having a body weight of about 70 kg, a dosage in the rangeof about 0.01 to about 100 mg per kilogram of body weight per day issufficient. The specific dosage used, however, can vary. For example,the dosage can depend on a number of factors including the requirementsof the patient, the severity of the condition being treated, and thepharmacological activity of the compound being used. The determinationof optimum dosages for a particular patient is well known to thoseskilled in the art.

The following examples are illustrative, but not limiting, of the methodand compositions of the present invention. Other suitable modificationsand adaptations of the variety of conditions and parameters normallyencountered and obvious to those skilled in the art are within thespirit and scope of the invention.

EXAMPLE 1 Diethyl 2-iodobenzylphosphonate (11)

A mixture of 2-iodobenzyl bromide 10 (5 g, 16.84 mmol) and triethylphosphite (3.3 g, 20 mmol) was stirred at 160° C. After 4 h, the mixturewas cooled to room temperature. The residue was subjected to flashchromatography (EtOAc: Hex, 1:4), and gave 2.3 g of 11 (39%). ¹H NMR(200 MHz, CDCl₃): δ1.24 (t, J=7.04 Hz, 6H), 3.40 (d, J=22.00 Hz, 2H),4.03 (m, 4H), 6.91 (m, 1H), 7.32 (m, 1H), 7.44 (m, 1H), 7.82 (m, 1H);¹³C NMR (50 MHz, CDCl₃): δ 16.27 (J=6.00 Hz), 38.31 (J=137.50 Hz), 62.16(J=6.70 Hz), 101.16 (J=9.45 Hz), 128.23 (J=3.35 Hz), 128.45 (J=3.55 Hz),130.60 (J=5.10 Hz), 135.36 (J=8.80 Hz), 139.60 (J=2.85 Hz).

EXAMPLE 2 (E)-2′-Iodo-N,N-dimethyl-4-stilbenamine (4)

To a mixture of NaH (2 mmol, 80% suspension in oil), and3-iodobenzylphosphonate 2 (500 mg, 1.42 mmol) in 6 mL of THF at 80° C.under nitrogen atmosphere, was added dropwise4-(dimethylamine)benzaldehyde (210 mg, 1.41 mmol). After overnight atroom temperature, NH₄Cl solution (saturated, 5 mL) was added and themixture was extracted with CH₂Cl₂ (3×30 mL). The combined organicextract was dried over Na₂SO₄ and evaporated to give(E)-2′-iodo-N,N-dimethyl-4-stilbenamine 11, which was purified by flashchromatography (EtOAc: Hex, 1:9) to give 3 (330 mg, 67%). ¹H NMR (200MHz, CDCl₃): δ 3.06 (s, 6H), 6.82 (m, 2H), 6.93–7.02 (m, 1H), 7.01 (d,J=15.98 Hz, 1H), 7.25 (d, J=15.99 Hz, 1H), 7.40 (m, 1H), 7.53–7.59 (m,2H), 7.69 (dd, J=7.88 Hz, J=1.54 Hz, 1H), 7.95 (dd, J=7.92 Hz, J=1.20Hz, 1H); ¹³C NMR (50 MHz, CDCl₃): δ 40.26, 100.20, 112.22, 125.12,125.61, 127.83, 127.87, 127.97, 128.2, 131.66, 139.42, 140.84, 150.23;HRMS: m/z Calcd for C₁₆H₁₆IN: 349.0328; Found: 349.0342.

EXAMPLE 3 Diethyl 3-iodobenzylphosphonate (13)

A mixture of 3-iodobenzyl bromide 12 (5 g, 16.84 mmol) and triethylphosphite (3.3 g, 20 mmol) was stirred at 160° C. After 4 h, the mixturewas cooled to room temperature. The residue was subjected to flashchromatography (EtOAc: Hex, 1:4), and gave 5.4 g of 13 (91%). ¹H NMR(200 MHz, CDCl₃): δ1.15 (t, J=7.05 Hz, 6H), 2.97 (d, J=21.65 Hz, 2H),3.92 (m, 4H), 6.93 (t, J=7.76 Hz, 1H), 7.17 (m, 1H), 7.52 (m, 2H); ¹³CNMR (50 MHz, CDCl₃): δ 16.25 (J=5.95 Hz), 33.15 (J=137.60 Hz), 62.19(J=6.70 Hz), 94.13 (J=3.50 Hz), 128.89 (J=6.35 Hz), 130.07 (J=3.00 Hz),133.95 (J=9.10 Hz), 135.87 (J=3.55 Hz), 138.51 (J=6.65 Hz).

EXAMPLE 4 (E)-3′-Iodo-N,N-dimethyl-4-stilbenamine (5)

To a mixture of NaH (2 mmol, 80% suspension in oil), and3-iodobenzylphosphonate 13 (370 mg, 1.05 mmol) in 5 mL of THF at 80° C.under nitrogen atmosphere, was added dropwise4-(dimethylamine)benzaldehyde (155 mg, 1.05 mmol). After overnight atroom temperature, NH₄Cl solution (saturated, 5 mL) was added and themixture was extracted with CH₂Cl₂ (3×20 mL). The combined organicextract was dried over Na₂SO₄ and evaporated to give(E)-3′-iodo-N,N-dimethyl-4-stilbenamine 5, which was purified by flashchromatography (EtOAc: Hex, 1:9) to give 3 (209 mg, 57%). ¹H NMR (200MHz, CDCl₃): δ 2.99 (s, 6H), 6.71 (m, 2H), 6.77 (d, J=16.41 Hz, 1H),7.02 (d, J=16.22 Hz, 1H), 7.04 (t, J=7.8 Hz, 1H), 7.36–7.52 (m, 4H),7.82 (s, 1H); ¹³C NMR (50 MHz, CDCl₃): δ 40.37, 94.78, 112.38, 112.53,122.21, 127.76, 128.56, 130.19, 134.76, 135.34, 140.56, 150.36; HRMS:m/z Calcd for C₁₆H₁₆IN: 349.0328; Found: 349.0302.

EXAMPLE 5 Diethyl 4-iodobenzylphosphonate (15)

A mixture of 4-iodobenzyl bromide 14 (5.2 g, 17.51 mmol) and triethylphosphite (3.3 g, 20 mmol) was stirred at 160° C. After 4 h, the mixturewas cooled to room temperature. The residue was subjected to flashchromatography (EtOAc: Hex, 1:4), and gave 3.27 g of 15 (53%). ¹H NMR(200 MHz, CDCl₃): δ1.24 (t, J=7.04 Hz, 6H), 3.07 (d, J=21.72 Hz, 2H),4.01 (m, 4H), 7.04 (m, 2H), 7.62 (m, 2H); ¹³C NMR (50 MHz, CDCl₃): δ16.24 (J=5.90 Hz), 33.21 (J=137.55 Hz), 62.04 (J=6.70 Hz), 92.15 (J=4.80Hz), 131.31 (J=9.10 Hz), 131.57 (J=6.55 Hz), 137.43 (J=2.95 Hz).

EXAMPLE 6 (E)-4′-Iodo-N,N-dimethyl-4-stilbenamine (6)

To a mixture of NaH (2 mmol, 80% suspension in oil), and4-iodobenzylphosphonate 15 (420 mg, 1.19 mmol) in 5 mL of THF at 80° C.under nitrogen atmosphere, was added dropwise4-(dimethylamine)benzaldehyde (180 mg, 1.20 mmol). After overnight atroom temperature, water (5 mL) was added. The solid formed was filteredand washed with ether to give crude 6 which was purified byrecrystallization with CH₂Cl₂/hexane to afford pure 6 (156 mg, 38%). ¹HNMR (200 MHz, CDCl₃): δ 2.99 (s, 6H), 6.71 (d, J=8.60 Hz, 2H), 6.81 (d,J=16.65 Hz, 1H), 7.04 (d, J=16.12 Hz, 1H), 7.21 (d, J=8.15 Hz, 1H), 7.38(d, J=8.59 Hz, 2H), 7.63 (d, J=8.28 Hz, 2H); ¹³C NMR (50 MHz, CDCl₃): δ40.39, 91.32, 112.38, 123.04, 127.69, 127.73, 128.23, 129.65, 137.55,137.77, 150.29; HRMS: m/z Calcd for C₁₆H₁₆IN: 349.0328; Found: 349.0288.

EXAMPLE 7 (E)-4′-Iodo-4-O-methoxystilbenol (8)

To a mixture of NaH (2 mmol, 80% suspension in oil), and3-iodobenzylphosphonate 13 (450 mg, 1.27 mmol) in 7 mL of THF at 80° C.under nitrogen atmosphere, was added dropwise p-anisaldehyde (172 mg,1.27 mmol). After 3 days at room temperature, NH₄Cl solution (saturated,5 mL) was added and the mixture was extracted with CH₂Cl₂ (3×30 mL). Thecombined organic extract was dried over Na₂SO₄, evaporated and purifiedby flash chromatography (EtOAc: Hex, 1:9) to give(E)-1-iodo-3-[2-(4-methoxyphenyl)ethenyl] benzene 8 (400 mg, 90%). ¹HNMR (200 MHz, CDCl₃): δ 3.84 (s, 3H), 6.84 (d, J=16.29 Hz, 1H), 6.90 (m,2H), 7.05 (d, J=16.30 Hz, 1H), 7.07 (t, J=7.8 Hz, 1H), 7.42–7.56 (m,4H), 7.85 (s, 1H); ¹³C NMR (50 MHz, CDCl₃): δ 55.32, 94.76, 114.20,124.85, 125.48, 127.88, 129.58, 129.62, 130.25, 135.00, 135.91, 139.97,159.62; HRMS: m/z Calcd for C₁₅H₁₃IO: 336.0011; Found: 336.0006.

EXAMPLE 8 (E)-3′-Iodo-4-stilbenol (9)

To a solution of 8 (350 mg, 1.00 mmol) in CH₂Cl₂ (200 mL) was added BBr₃(10 mL, 1M in hexane) dropwise at −78° C. in a dry ice-acetone bath. Themixture was allowed to warm up to room temperature. Water was addedwhile the reaction mixture was cooled at 0° C. in an ice bath. Themixture was extracted with CH₂Cl₂. The organic phase was dried andfiltered. The filtrate was purified by flash chromatography (EtOAc: Hex,1:9) to give 9 (296 mg, 92%). ¹H NMR (200 MHz, CDCl₃): δ 4.81 (s, 1H),6.83 (d, J=16.17 Hz, 1H), 6.84 (m, 2H), 7.03 (d, J=16.32 Hz, 1H), 7.06(t, J=7.8 Hz, 1H), 7.36–7.57 (m, 4H), 7.84 (s, 1H); ¹³C NMR (50 MHz,CDCl₃): δ 94.75, 115.67, 124.96, 125.49, 128.09, 129.48, 129.87, 130.25,135.01, 135.96, 139.90, 155.53; HRMS: m/z Calcd for C₁₄H₁₁IO: 321.9855;Found: 321.9840.

EXAMPLE 9 Diethyl, 4-fluorobenzylphosphonate (17)

A mixture of 4-fluorobenzyl bromide 16 (1.89 g, 10 mmol) and triethylphosphite (1.66 g, 10 mmol) was stirred at 170° C. for 4 h. The mixturewas cooled to room temperature. and the residue was subjected to flashchromatography (EtOAc: Hex, 1:4) to gave 1.4 g of 17(57%). ¹H NMR (200MHz, CDCl₃): δ 1.23 (t, J=7.1 Hz, 6H), 3.10 (d, J=21.4 Hz, 2H), 3.92 (q,J=7.1 Hz, 4H), 7.02 (m, 2H), 7.25 (m, 2H).

EXAMPLE 10 (E)-4-Fluoro-4′-dimethylamino-stilbene (7)

To a mixture of phosphate 17 (246 mg, 1 mmol) and4-dimethylaminobenzaldehyde (149 mg, 1 mmol) in DMF (2 mL) was addedKO^(t)Bu (224 mg, 2 mmol) in portions in solid form at RT. The resultingmixture was stirred at RT overnight. Water (10 mL) was added The solidwas collected by suction and washed with water, dried to give 190 mg ofproduct (80%).

¹H NMR (200 MHz, CDCl₃): δ 2.99 (s, 6H), 6.71 (d, J=8.9 Hz, 2H), 6.85(d, J=16.3 Hz, 1H), 7.01 (t, J=8.7 Hz, 2H), 7.40 (d, J=9.0 Hz, 2H), 7.43(m, 2H); ¹³C NMR (200 MHz, CDCl₃): δ 41.00, 113.01, 115.78, 116.21,123.76, 126.18, 127.83, 127.99, 128.05, 129.19, 134.91, 150.72, 164.81.

EXAMPLE 11 (E)-3-Tributylstannyl-4′-dimethylamino-stilbene (18)

A mixture of 5 (139 mg, 0.38 mmol), bis-(tributytyltin) (0.4 mL) andPd(Ph₃P)₄ (30 mg) in a mixed solvent (20 mL, dioxane:triethylamine, 3:1)was stirred at 90° C. overnight. Solvent was removed and the residue waspurified by PTLC (Hex:EtOAc, 2:1) to give 35 mg of product (18%, notoptimized yield). ¹H NMR (200 MHz, CDCl₃): δ 0.94 (t, J=7.2 Hz, 9H),1.08–1.66 (m, 18H), 3.01 (s, 6H), 6.75 (m, 2H), 6.94 (d, J=16.3 Hz, 1H),7.08 (d, J=16.3 Hz, 1H), 7.25–7.57 (m, 6H); ¹³C NMR (50 MHz, CDCl₃): δ9.56, 13.67, 27.37, 29.10, 40.45, 112.45, 124.84, 125.44, 125.98,127.51, 128.01, 128.51, 134.36, 134.89, 137.41, 142.09, 150.06; HRMS:m/z Calcd for C₂₈H₄₄NSn (MH⁺): 514.2496; Found: 514.2512.

EXAMPLE 12 Preparation of Radioiodinated Ligand

The desired ¹²⁵I-labeled compound was prepared using iododestannylationreactions with tributyltin precursor of 5. Hydrogen peroxide (50 μL, 3%w/v) was added to a mixture of 50 μL of the corresponding tributyltinprecursor, 18, (1 μg/μL EtOH), 50 μL of 1N HCl and [¹²⁵I]NaI (1–5 mCi)in a closed vial. The reaction was allowed to proceed for 10 min at roomtemperature and terminated by addition of 100 μL of sat. NaHSO₃. Thereaction mixture was extracted with ethyl acetate (3×1 mL) afterneutralization with saturated sodium bicarbonate solution. The combinedextracts were evaporated to dryness. The residue was dissolved in 100 μLof EtOH and purified by HPLC using a reversed phase column (Waters C-18ubondpad, 3.9×300 mm) with an isocratic solvent of 80% acetonitrile-20%of buffer, 3,3-dimethylglutaric acid (5 mM, pH 7.0) in a flow rate of0.8 mL/min. The desired fractions containing the product were collected,condensed and re-extracted with ethyl acetate. The no-carrier-addedproduct was evaporated to dryness and re-dissolved in 100% EtOH (1μCi/μL), The final ¹²⁵I probe, with a specific activity of 2,200Ci/mmole and a greater than 95% radiochemical purity, was stored at −20°C. up to 6 weeks for in vitro binding studies.

EXAMPLE 13 Binding Assays Using Aggregated Aβ(1–40) Peptide in Solution

The solid forms of peptides Aβ(1–40) was purchased from Bachem (King ofPrussia, Pa.). Peptide aggregation was carried out by gently dissolvingthe peptide (0.5 mg/mL) in a buffer solution (pH 7.4) containing 10 mMsodium phosphate and 1 mM EDTA. The solution was incubated at 37° C. for36–42 h with gentle and constant shaking. Binding studies were carriedout in 12×75 mm borosilicate glass tubes according to the proceduredescribed¹. Aggregated fibrils (10–50 nM in the final assay mixture)were added to the mixture containing 50 μl of radioligands (0.01–0.5 nMin 40% EtOH) and 10% EtOH in a final volume of 1 mL for saturationstudies. The final concentration of EtOH was 10%. Nonspecific bindingwas defined in the presence of 2 μM thioflavin T. For inhibitionstudies, 1 mL of the reaction mixture contained 40 μl of inhibitors(10⁻⁵–10⁻¹⁰ M in 10% EtOH) and 0.05 nM radiotracer in 40% EtOH. Themixture was incubated at room temperature for 3 h and the bound and thefree radioactivities were separated by vacuum filtration through WhatmanGF/B filters using a Brandel M-24R cell harvester followed by 2×3 mLwashes of 10% ethanol at room temperature. Filters containing the boundI-125 ligand were counted in a gamma counter (Packard 5000) with 70%counting efficiency. Under the assay conditions, the percent of thespecifically bound fraction was less than 20% of the totalradioactivity. The results of saturation and inhibition experiments weresubjected to nonlinear regression analysis using software EBDA² by whichK_(d) and K_(i) values were calculated. Values for (K_(i), nM) are themean±SEM of three independent experiments, each in duplicate. AdditionalK_(i) values for compounds of Formula I are provided in FIGS. 1 and 2.

In in vitro binding assays using pre-formed Aβ aggregates of syntheticpeptides and [¹²⁵I]TZDM as the ligand, these novel stilbenes showedexceedingly high binding affinity (2–40 nM) to the TZ sites, while theaffinity towards SB sites was very low (>1,000 nM). It is evident thatthe stilbenes containing an electron donating groups, such asdimethylamino-, —OH or —OMe group, showed excellent binding affinity toAβ aggregates. Benzothiazole ring appears to be unnecessary for bindingat the TZ binding sites of Aβ aggregates. This information is ofparamount importance because it reduces the molecular size (molecularweight of TZDM and 1 was 380 and 349, respectively) required for bindingto the TZ sites; as such it significantly enhances the flexibility ondesigning new ligands. The idoinated stilbenes, such as 2 and 5,respresent a structural simplicity, which suggests minimum requirementsfor binding the Aβ aggregates may be three: 1) two benzene ringsseparated by a vinyl group. 2) one of the aromatic ring contains aelectronic negative group, dimethylamino-, —OH or —OMe group. 3) thereappears to be a bulk tolerance for substitution on the second aromaticring. To characterize the compounds further, radioactive iodinatedligand, [¹²⁵I]2, was prepared by converting the correspondingtributyltin derivative in the presence of Na[¹²⁵I]I and hydrogenperoxide, by which the no-carrier added product was obtained inexcellent yield (radiochemical purity >95%). The direct binding assayshowed that the new evaluation of postmortem AD brain sections with[¹²⁵I]2 suggested that the novel ligand, as expected, labeled Aβplaques.

EXAMPLE 14 In vivo Biodistribution of New Probes in Normal Mice

While under ether anesthesia, 0.15 mL of a saline solution containingthe labeled agent (5–10 μCi) was injected directly into the tail vein ofICR mice (2–3 month-old, average weight 20–30 g). The mice weresacrificed by cardiac excision at various time points post injection.The organs of interest were removed and weighed, and the radioactivitywas counted with an automatic gamma counter (Packard 5000). Thepercentage dose per organ was calculated by a comparison of the tissuecounts to suitably diluted aliquots of the injected material. Totalactivities of blood and muscle were calculated under the assumption thatthey were 7% and 40% of the total body weight, respectively.

In vivo biodistribution study of [¹²⁵I]2 in normal mice after an ivinjection suggested good brain penetration. The brain uptake was 0.84,1.08, 0.91, and 0.54% dose/organ, at 2, 30, 60 and 120 minutes afterinjection (the blood levels was relatively low 5.2–3.6% dose/organ atall of the time points). Radioactive ligand's binding to the aggregatesof Aβ₁₋₄₀ is saturable and the K_(d) was 0.2 nM.

Having now fully described this invention, it will be understood tothose of ordinary skill in the art that the same can be performed withina wide and equivalent range of conditions, formulations, and otherparameters without affecting the scope of the invention or anyembodiment thereof. All patents, patent applications, and publicationscited herein are fully incorporated by reference herein in theirentirety.

1. A compound of general Formula I:

or a pharmaceutically acceptable salt thereof, wherein: R⁵ is hydrogenor C₁₋₄ alkyl; R¹, R² and R³, in each instance, is independentlyselected from the group consisting of hydrogen, halogen, C₁₋₄ alkyl,cyano, carboxy(C₁₋₅)alkyl, trifluoromethyl, nitro, methylamino,dimethylamino, halo(C₁₋₄)alkyl, and formyl; R⁴ is selected from thegroup consisting of: a. C₁₋₄ alkylthio, b. halo(C₁₋₄)alkoxy, c.carboxy(C₁₋₅)alkyl, d. hydroxy, e. C₁₋₄ alkoxy, f. NR⁶R⁷, wherein R⁶ andR⁷ are hydrogen, fluoro(C₁₋₄)alkyl or C₁₋₄ alkyl, g. phenyl(C₁₋₄)alkyl,h. C₆₋₁₀ aryl, i. heteroaryl, j. heterocycle, k. heterocycle(C₁₋₄)alkyl,and l. C₃₋₆ cycloalkyl, wherein said phenyl(C₁₋₄)alkyl, C₆₋₁₀ aryl,heteroaryl, heterocycle, heterocycle(C₁₋₄)alkyl or C₃₋₆ cycloalkyl issubstituted with one of the following: C₁₋₄ alkylthio, C₁₋₄ alkylsulfonyl, methoxy, hydroxy, dimethylamino or methylamino; and, X′ is¹²⁵I, ¹²³I, ¹³¹I, ¹⁸F, ¹⁸Fluoro(C₁₋₄)alkyl,[¹⁸Fluoro(C₁₋₄)alkyl]amino,[¹⁸Fluoro(C₁₋₄)alkyl]alkylamino, ⁷⁶Br or ⁷⁷Br.
 2. A compound of claim 1,wherein R⁵ is hydrogen or methyl; and R³ is hydrogen.
 3. A compound ofclaim 1, wherein R¹ and R² are hydrogen or C₁₋₄ alkyl.
 4. A compound ofclaim 3, wherein R⁵ is hydrogen.
 5. A compound of claim 4, wherein R¹ ishydrogen, and R⁴ is C₁₋₄ alkylthio, halo(C₁₋₄)alkoxy, hydroxy, C₁₋₄alkoxy or NR⁶R⁷, wherein R⁶ and R⁷ are hydrogen, fluoro(C₁₋₄)alkyl orC₁₋₄ alkyl.
 6. A compound of claim 5, wherein R² is hydrogen.
 7. Acompound of claim 1, wherein R⁴ is methylthio, hydroxy, methoxy orNR⁶R⁷, wherein R⁶ and R⁷ are hydrogen, fluoro(C₁₋₄)alkyl or methyl.
 8. Acompound of claim 1, wherein X′ is ¹²³I. the other of R²⁹ and R³²represents an unsubstituted postion.
 9. A compound of claim 8, whereinX′ is ¹⁸Fluoromethyl, ¹⁸Fluoroethyl or ¹⁸Fluoropropyl.
 10. Apharmaceutical composition comprising a compound of claim
 1. 11. Adiagnostic composition for imaging amyloid deposits, comprising aradiolabeled compound of claim 1; and a pharmaceutically acceptableexcipient or diluent.
 12. A method of imaging amyloid deposits,comprising: a. introducing into a mammal a detectable quantity of adiagnostic composition of claim 11; and b. allowing sufficient time forthe labeled compound to be associated with amyloid deposits; and c.detecting the labeled compound associated with one or more amyloiddeposits.
 13. A method of inhibiting amyloid plaque aggregation in amammal, comprising administering a composition of claim 10 in an amounteffective to inhibit amyloid plaque aggregation.